Evidence suggests rhythmic whisker movements in rats are driven by a subcortical central pattern generator (CPG) under control of the whisker motor cortex (wMCx). Additionally, it has been demonstrated that serotonin (5HT) is necessary for whisking. My goal is to investigate a subset of 5HT neurons in the brainstem of adult rats that are likely to comprise an integral part of the whisking CPG. I will investigate the control exerted by the wMCx over this putative CPG component and the impact that the resulting CPG modulation has on whisking frequencies. I propose that the 5HT CPG determines firing frequency of whisker motor units by regulating the delivery of 5HT to motoneurons in the lateral facial nucleus. I further propose that 5HT regulates motor unit firing rates by facilitating a persistent inward current in whisker motoneurons (wMNs) in a dose dependent manner. I will investigate the ability of 5HT to facilitate a dose dependent PIC in whisker motoneurons and its relation to whisker motoneuron firing frequency. [unreadable] [unreadable] [unreadable]